PURPOSE: To provide a density detecting method for an image forming device capable of obtaining accurate density control information by improving density detecting sensitivity against the change of a toner amount.

CONSTITUTION: In this density detecting method for the image forming device where the latent image of a patch for adjusting image density formed on a photoreceptor 401 is developed with toner and the image density is adjusted according to the light reception output of reflected light being light projected to the developed toner image pacth 401a; the toner image patch 401a is a linear pattern, the optical axes of the projected light and the reflected light form a specified angle, and an angle α formed by a line obtained by crossing a plane including the optical axes of the projected light and the reflected light with the plane of the toner image patch 401a and the longitudinal direction of the linear pattern of the toner image patch is about 90°.